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5
Absolute Measurement Fundamentals
What Sets the Measurement Noise Floor?
The noise floor for your measurement is set by two things:
• The noise floor of the phase detector and low-noise amplifier (LNA)
• The noise level of the reference source you are using
The System Noise Floor
The noise floor of the system is directly related to the amplitude of the input
signal at the R input port of the system's phase detector. Table 11 shows the
amplitude ranges for the L and R ports.
Table 11 Amplitude ranges for L and R ports
Phase Detector
50 kHz to 1.6 GHz
Ref Input (L
Port)
1 Phase noise test set Options 001 and 201 with no attenuation.
2 Phase noise test set Option 001 with no attenuation.
If the L port (Reference Input) signal is within the amplitude range shown in
Table
system.
Figure 74
system noise floor.
E5505a_r_input_sys_noise
26 Feb 04 rev 1
Figure 74 Relationship between the R input level and system noise floor
110
1.2 to 26.5 GHz
Signal Input
Ref Input
(R Port)
(L Port)
11, the signal level at the R (Signal Input) port sets the noise floor for the
shows the relationship between the R (signal) input level and the
L Port level
+15
+5
-5
-15
-140
-150
Expected phase noise floor of phase detector and LNA (dBc/Hz)
1
50 kHz to 26.5 GHz
Signal Input
AM Noise
(R Port)
+15dBm
-160
-170
f
10kHz
2
-180
Agilent E5505A User's Guide
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